German Published Patent Application No. 195 20 300 and U.S. Pat. No. 5,715,786 discuss a method and a device for monitoring a fuel metering system of an internal combustion engine, in particular a common rail system. With such common rail systems, the fuel is compressed by a pump, and a pressure variable characterizing the fuel pressure is determined. A fault in the area of the fuel metering system is detected by monitoring the pressure signal in certain operating states.
Pressure is often generated by high-pressure pumps which are configured in particular as radial piston pumps including at least two to three pump elements. To reduce the pump delivery rate, each of these is provided with an element shutdown valve. A corresponding common rail system is discussed, for example, in the publication MTZ Motortechnische Zeitschrift 58 (1997) no. 10, page 572 ff.
Malfunctions may cause one of the pump elements or an element shutdown valve not to operate properly. Such a pump element failure may not be detected reliably with other monitoring systems. Such a pump element failure is detected reliably only when the pump delivery rate is no longer adequate to cover the quantity of fuel to be injected. This is the case in particular only when large quantities of fuel are injected.